The synthesis, properties and applications of lubricants are summarized in a monograph entitled "Lubricants and Related Products" by Dieter Klamann. This book, published by Verlag Chemie, Weinheim, W. Germany in 1984 has a chapter (pages 96 to 106) which specifically discusses synthetic hydrocarbon lubricants, including those derived from olefins. As such the chapter and its citations are incorporated into this memorandum by reference. Some of the key patents and publications are discussed in the following. Although this discussion is largely contrasting the prior art with the multistep manufacturing process for lubricants of the present invention, the description of the single steps of prior art processes also provides information applicable in the practice of the present invention and a such is incorporated into the present application by reference.
The preparation of synthetic lubricants via olefin oligomerization in general is well known in the prior art. J. A. Brennan of Mobil published an early review of the literature in the journal, Ind. Eng. Chem., Prod. Res. Dev. Vol. 19, pages 2-6 in 1980 and the references of this article. Brennan particularly investigated the oligomerization of even carbon number .alpha.-olefins from ethylene. His work was aimed at getting isoparaffins of wide temperature range fluidity via the hydrogenation of the oligomer intermediates. Based on this work, he concluded that decene trimers obtained via BF.sub.3 catalyzed oligomerization provide superior lubricant fluids on hydrogenation. Such trimers are a main component of the commercial Mobil 1 synthetic lubricant.
While 1-decene based synthetic hydrocarbon lubricants have excellent quality, their economics of manufacture are unfavorable. 1-Decene is only one of the products of ethylene oligomerization. Therefore, its availability is limited and its price is very high. There is a great need for other synthetic hydrocarbon lubricants of greater availability and lesser cost.
The above referred Brennan publication and an article by Onopchenko, Cupples and Kresge in Ind. Eng. Chem., Prod. Res. Dev. Vol. 2, pages 182-191 in 1983 discussed the structures of various potential hydrogenated polyolefin lubricant candidates and correlated them with their low temperature behavior characterized by solidification temperatures or pour points and wide temperature behavior indicated by their viscosity indices. They found that isoparaffins having short n-alkyl segments had outstanding low temperature behavior, but poor viscosity characteristics. In contrast, long n-alkyl segments assure desirable viscosity but lead to poor low temperature behavior. The design of lubricants having balanced properties apparently calls for an innovative compromise in molecular design. It appears that isoparaffins in the C.sub.25 to C.sub.60 carbon range per molecule are good lubricant candidates, if they have 1 to 3 alkyl side chains of medium chain length on the n-alkane carbon skeleton as close to the center of the molecule as possible.
One of the prior art approaches to isoparaffins of improved economics is described by Petrillo et. al. in U.S. Pat. No. 4,167,534. According to this patent, the feed for oligomerization is C.sub.11 to C.sub.14 mixture of n-olefins having double bonds statistically distributed along the entire chain. Such olefins are obtained via the dehydrogenation of the corresponding paraffins as prepared by the ISOSIV process and are utilized as the feed. Oligomerization is carried out in the presence of a Friedel Crafts catalyst, preferably AlCl.sub.3. The hydrogenated oligomers have an excellent low temperature behavior, i.e. pour points of -50.degree. C. or lower and kinematic viscosities at 40.degree. C. in the range of about 30 to 40 centistokes.
Another approach to synthetic lubricants is disclosed by L. Heckelsberg in U.S. Pat. No. 4,317,948 assigned to Phillips Petroleum Co. In the first step, Heckelsberg produces an internal olefin, preferably via metathesis of an .alpha.-olefin. In the second step, the internal olefin is codimerized with an .alpha.-olefin. For example, 1-dodecene, is converted to a 11-docosene which is then isolated and codimerized with 1-dodecene to provide C.sub.34 isoolefins: ##STR1## U.S. Pat. No. 4,319,064 by Heckelsberg et. al. discloses the dimerization of BF.sub.3 based catalysts of internal olefin dimer fractions obtained via the metathesis of C.sub.8, C.sub.10 and C.sub.12 .alpha.-olefins. Another method based on the metathesis of .alpha.-olefins is disclosed in U.S. Pat. No. 4,300,006 by W. T. Nelson, also assigned to Phillips. This patent describes the boron trifluoride catalyzed codimerization without prior separation of the components of a .alpha.-olefin metathesis reaction mixtures. The products of both the Heckelsberg and the Nelson patents have pour points in the range of about -32 to -54.degree. C. and 40.degree. C. viscosities of 100 to 133 cst.
A large number of patents have issued covering the oligomerization of linear olefins in the C.sub.6 to C.sub.25 range to lubricants. Most of them employ even carbon .alpha.-olefins as a feed. However, a few patents disclose the use of cracked wax olefins.
U.S. Pat. No. 1,955,200 by Sullivan, Jr. and Voorhees, assigned to Standard Oil Co. of Indiana, discloses the synthesis of a stable, high VI lube oil via wax cracking followed by polymerization in the presence of AlCl.sub.3 as a catalyst.
U.S. Pat. No. 3,883,417, by C. Woo and J. A. Bichard, assigned to Exxon, describes a two stage process for the production of lube oils by the thermal polymerization of the olefin components of steam cracked paraffin waxes and gas oils. In the first stage, the more reactive components such as diolefins are polymerized. A distillate containing the less reactive .alpha.-olefin components is separated from the reaction mixture and converted to lubricants of high viscosity index.
U.S. Pat. No. 3,156,736 assigned to Shell also utilized cracked wax olefins for producing lubricants. In the Shell process C.sub.9 to C.sub.17 cracked wax olefins are first separated by urea clathration. Then they are purified by percolation over silica gel. The pure olefins are polymerized using an aluminum trialkyl - titanium tetrachloride catalyst system. The C.sub.30 and higher distillate product fraction is hydrogenated to provide the lubricant product. Another U.S. Patent to Shell, No. 2,051,612 describes a process for the preparation of a suitable olefin feed for lube oil manufacture. According to this patent a paraffinous oil provides the desired olefins in a two stage cracking process.
Various acid catalysts an Ziegler-Natta type catalyst systems as well as thermal processes were utilized to oligomerize higher olefins to lubricant intermediates. Boron trifluoride based catalyst systems were most extensively investigated. U.S. Pat. No. 2,816,944 by Muessig and Lippincott to Exxon disclosed the use of a BF.sub.3 -H.sub.3 PO.sub.4 system for the oligomerization of C.sub.6 to C.sub.25 olefins. U.S. Pat. No. 3,382,291, by Brennan to Mobil describes a process for the oligomerization of C.sub.5 to C.sub.20 .alpha.-olefins, preferably 1-decene in the presence of BF.sub.3 plus a 1:1 BF.sub.3 complex of water, alcohol, acids, ethers, esters, aldehydes, and ketones. Another Mobil patent, i.e. U.S. Pat. No. 3,769,363, specifically claims the oligomerization of C.sub.6 -C.sub.12 olefins with BF.sub.3 pentanoic acid complexes. In U.S. Pat. No. 4,213,001, by Madgavkar et. al. assigned to Gulf, the oligomerization of C.sub.6 to C.sub.12 .alpha.-olefins in the presence of BF.sub.3 treated adsorbent silica is claimed. U.S. Pat. No. 4,218,330, by Shubkin to Ethyl Corp. specifically discloses the dimerization of C.sub.12 to C.sub.18 .alpha.-olefins in the presence of boron trifluoride hydrate. A similar process using a perfluorosulfonic acid resin Nafion alone or complexed with BF.sub.3 is disclosed in U.S. Pat. Nos. 4,367,352 and 4,400,565, assigned to Texaco. For the oligomerization of linear olefins containing major amounts of less reactive internal isomers U.S. Pat. No. 4,420,646, by Darden, Walts and Marquis of Texaco, discloses the use of a promoted BF.sub.3 catalyst 17,082, also from Texaco, describes the cooligomerization of C.sub.3 -C.sub.5 and C.sub.8 -C.sub.18 .alpha.-olefins with a similar catalyst system at close to ambient temperature.
As indicated above the linear olefin feeds for lubricant synthesis of the prior art were mostly derived via ethylene polymerization. These feeds did not require the application of olefin separation processes. The only relatively complex feeds employed were cracked distillates. These contained a mixture of mostly linear olefins but no aromatics and sulfur compounds. As it will be discussed the linear olefin and paraffin components of cracked wax were separated via urea adduction to produce feeds for synthetic lubricants. Urea adduction is also applicable to the thermally cracked, residua derived feeds of the present process.
The urea adduction method for the separation of straight chain hydrocarbons and monosubstituted derivatives was discovered by Bengen in Germany during World War II (see German Patent No. 869,070). This method was commercially developed, primarily for the dewaxing of mineral oil fractions, i.e. the separation of n-paraffins from hydrocarbon mixtures of aliphatic character. This development was reviewed by Alfred Hoppe of Edeleanu Gmbh, in Chapter 4, pages 192 to 234 of Volume 8 of a series of monographs on "Advances in Petroleum Chemistry and Refining" edited by J. J. McKetta Jr., and published by Interscience Publishers of J. Wiley & Sons, New York, 1964. The urea adducts of straight chain paraffins and olefins which are of special petrochemical interest were described by Schlenk, Jr. in Fortschritte de Chemischen Forschung, Volume 2, page 92 in (1951), by E. Terres and S. Nath Sur in Brennstoff-Chemie, Volume 38, pages 330 to 343 in I957 and by W. G. Domagk and K. A. Kobe in Petroleum Refiner, Volume 34, No. 4, pages 128-133 in 1955.
The urea adduction method was employed for the separation of o-olefins as well as n-paraffins. L. C. Fetterly discussed the separation of .alpha.-olefin - n-paraffin mixtures via urea adduction from cracked wax, thermally cracked gas oil and naphtha in Petroleum Refiner, No. 4, pages 128-133 in 1955. Such separations were disclosed in detail by Garner et. al. in U.S. Pat. No. 2,528,677 assigned to Shell, by Woodbury in U.S. Pat. No. 2,642,421 assigned to Socony-Vacuum Oil and by Goldsbrough of Shell at the 1955 World Petroleum Congress, Rome, in Section III/B, Paper 4. Reference to the recovery of straight chain olefins from cracked stocks via urea adduction is also made by Bailey et. al. in Ind. Eng. Chem., Vol. 43, pages 2125-2129 in 1951. Also, German Patent 3,436,289-A, assigned to Council of Scientific and Industrial Research in New Delhi, discloses the separation via urea adduction of the .alpha.-olefin plus n-paraffin components of coker distillates derived via cracking crude oil fractions. The patent also states that the separated olefins are useful among others in the production of synthetic lubricants. However, the coker distillates employed were apparently of low sulfur content. The patent states that sulfur compounds inhibit urea adduct formation and thus teaches away from the present invention.
Urea adduction was employed commercially for the separation of n-paraffins in dewaxing. Several processes were developed on a pilot plant scale. In Petroleum Refiner, Volume 36, No. 7, pages 147-152 in 1957, Fetterly reviewed the commercial urea adduction units. Most of the details are provided in the previously cited Hoppe review. The basic features of these processes are discussed in the following since they are applicable to the coker distillate feeds of the present process.
Standard Oil Co. (Indiana) operated a dewaxing unit for the production of lubricating oil. The chemical basis of this unit has been described by Zimmerschied and coworkers in Ind. Eng. Chem., Vol 42, pages 1300-1396 in 1950. This publication and Fetterly's review point out that petroleum fractions usually fail to form adducts in the absence of an activator due to the presence of inhibitors, e.g. sulfur compounds etc.. In the Indiana process, probably methanol was used as an activator solvent.
Deutsche Erdoel produced low-pour diesel oil spindle oil via urea adduction as described by Hoppe in Erdoel und Kohle, Vol. II, pages 618 to 621 in 1958. The process employed was designed by Edeleanu and employed an aqueous reactant solution. A variant of the Edeleanu process using an aqueous isopropanol solution of urea was developed in Russia and has been described by J. Bathory in Chem.-Anlagen Verfahren, No. 3, pages 43 to 46 in 1972.
A process first employed by Sonneborn and Sons to produce white oil employed a crystalline urea reactant. This type of a process was more recently also developed by Nippon Mining and Chiyoda Chem. Eng. and Constr. Co.. Under the name Nurex, the process was designed for producing a n-paraffin feed for single protein production. The Nurex process was described in Bull. of the Japan Petr. Inst , Vol 8, June 7-12 issue (1966), the oil and Gas J., Vol. 70, No. 4, pages 141, 142 in 1972. A detailed comparison of the Nurex process with the Edeleneau process was made in the previously referred journal article by Bathory.
Shell Oil Co. developed a process applicable for the separation of the .alpha.-olefin and n-paraffin components of cracked wax which was described by the earlier quoted Bailey et. al., paper in Ind. Eng. Chem., a paper in the Proceedings of the 2nd World Petr. Congr., Hague, Sect. III, pages 161-171 also by Bailey et. al. and another paper by Goldsbrough which was also referenced earlier. This process employs both an organic solvent, methyl i-butyl ketone, and water and obtains the urea adducts by phase separation rather than filtration. Societe Francais des Petroles also developed a process based on the same phase separation principle.
Finally, a separation process using urea in partition chromatography was also disclosed in U.S. Pat. No. 2,912,426 assigned to Gulf. This process was successfully employed as an analytical technique for the determination of the major .alpha.-olefin and n-paraffin components of coal tar pitch (See Karr and Comberiati, J. Chromatog., Vol. 18, No. 2, pages 394-397, 1965).
The straight chain hydrocarbon components of distillate by-products of the thermal cracking of petroleum residua, with superheated steam to produce pitch to replace coking coal, were separated by the urea adduction process for analytical studies. This was reported by Ohnuma et. al. in J. Japan Petrol. Inst., Vol. 21, pages 28-34 in 1978. From a light oil fraction of 49% oil content up to 25% yields of linear hydrocarbons were obtained. Gas chromatography showed that these consisted mostly of n-paraffins (about 70%) and 1-n-olefins (20%). The minor components were I-methylparaffins and internal n-olefins.
European Patent Application No. 164,229 by Atsushi et. al. assigned to Nippon Petrochemicals Company disclosed a method of upgrading to paraffins thermally cracked distillate products derived from petroleum residua. According to this method, the olefin components of the distillate are reacted with the aromatic components to produce alkylaromatic compounds in the presence of an acid catalyst in the first step. The unreacted, paraffin rich components of the feed are then separated by distillation from the reaction mixture in the second step. The n-paraffins could then be isolated via urea adduction or by molecular sieve.
Aboul-Gheit, Moustafa and Habib reported, (in Erdoel und Kohle-Erdgas, Vol. 36, page 462 to 465 in 1985), the isolation in 30% yield of a linear hydrocarbon mixture consisting 35.6% n-olefins and 64.4% paraffins from a C.sub.11 to C.sub.14 coker distillate fraction containing 43.0% olefins and 29.1% saturates. They utilized the product to prepare a linear alkylbenzene detergent intermediate by the alkylation of benzene in the presence of a silicotungstic acid catalyst. However, they neither disclosed nor suggested the use of the olefin components of the products for the synthesis of lubricants.
An alternative method of separating the .alpha.-olefin and n-paraffin components of coker distillates is crystallization. No positive teaching could be found in the literature on the direct separation of n-paraffins plus 1-n olefins by crystallization from any feed. U.S. Pat. No. 3,691,246 by L. C. Parker, T. A. Cooper and J. L. Meadows described the selective crystallization of n-paraffins from methylethyl ketone solutions of sharp distillate fractions of cracked wax consisting of n-paraffins and n-olefins. Similarly, U.S. Pat. No. 3,767,724 by Tan Hok Gouw disclosed the selective crystallization of paraffins from CO.sub.2 solutions of olefin-paraffin mixtures. A journal publication by Von Horst Gundermann, Josef Weiland and Bernd Speckelsen [Erdoel and Kohle-Erdgas, Vol 24, No. 11, pages 696 to 701, (1971)] described the crystallization of C.sub.16 -C.sub.20 n-olefin plus n-paraffin mixtures from methylnaphthalene. The formation of n-paraffin crystals was reported. The authors concluded that for the crystallization of n-olefins always significantly lower temperatures are required than for that of the corresponding n-paraffins. Thus, this paper also taught away from the cocrystallization of these components.
There is much literature on the extraction of various petroleum distillates, particularly for the production of aromatic hydrocarbon extracts. However, there is no specific information on the extraction of coker distillates. The extraction of light aromatic hydrocarbons (BTX) from petroleum distillates with polar solvents, particularly sulfolane, is reviewed in a paper presented on "The Sulfolane Extraction Process" by H. Voetter and W. C. Kosters before the Sixth World Petroleum Congress in June 1963 (Paper No. III in Section II, pages 131 to 145). This extraction process was apparently limited to the use of highly aromatic catalytic reformates, pyrolysis gasoline and coke oven gasoline. In contrast to these feeds, the gasoline range feed of the present invention has a relatively low percentage of aromatics and high percentage of straight chain aliphatic hydrocarbons, largely 1-n-olefins. While the process of the prior art was simply directed to BTX production, aliphatic hydrocarbons, particularly olefins, are important coproducts of the present process. These aliphatic hydrocarbon rich fractions are for example advantageously used as feeds in the urea adduction process.
U.S. Pat. No. 3,755,15 by H. Akayabashi, S. Hoshiyama and S. Takigawa disclosed that acetylpyrrolidone and its solvent mixtures are uniquely suitable compared to sulfolane and other known solvents for the stepwise extraction of cracked petroleum oils of undefined origin. In the first step, the aromatic hydrocarbons are extracted, in the second the olefins and naphthenes. In contrast, for the separation of thermally cracked petroleum residua, sulfolane and similar solvents were found to be effective in the present work.
U.S. Pat. No. 4,267,034 by C. O. Carter described the selective extraction by dimethyl sulfoxide-water mixtures of the olefin components of olefin-paraffin mixtures. A similar olefin extraction by alcoholic solutions of silver and copper salts is claimed in U.S. Pat. No. 4,132,747 by John F. Knifton.
No separation processes using solid adsorbents were disclosed for thermally cracked residua of high sulfur and unsaturates content to our knowledge. U.S. Pat. No. 4,517,402 by R. N. Dessau describes a process for the selective sorption of linear aliphatic compounds from vacuum gas oil by ZSM-11 type zeolites. This Dessau patent and the patents cited therein, particularly U.S. Pat. No. 3,709,979, indicate that for such separation zeolites having appropriately small pore dimension and high silica to alumina ratios are used. Most of these zeolites were used for catalytic dewaxing as described in U.S. Pat. Nos. 3,894,938; 4,149,960. As such they do not suggest the separation of a highly reactive feed such as a coker distillate without concurrent reaction.
Eluent chromatography using highly polar solids such as silica gel was employed widely in petroleum chemistry as an analytical method for determining the types of compounds present. For example, the analysis of olefin-paraffin and aromatic hydrocarbon mixtures derived by wax cracking is described using such a method by E. Kh. Kurashova, I. A. Musayev, P. I. Sanin and A. N. Rumyantsev in Neftekhimiya, Vol. 7, No. 4, pages 519 to 529 in 1967. However, these applications were analytical rather than methods for producing components for industrial utilization.
In contrast to the prior art, the present invention starts with linear olefinic products of the high temperature thermal cracking of petroleum residua, separates the straight chain hydrocarbons of such cracked distillates and oligomerizes the linear olefin components to liquid polyolefin lubricant intermediates.
The final step in synthetic lubricant manufacture is the hydrogenation of polyolefins. Since the polyolefin intermediates of the prior art contained no sulfur compounds as impurities, generally sulfur sensitive metal catalysts of hydrogenation were employed. For example, the previously discussed U.S. Pat. No. 4,420,646 by Darden et. al. particularly prefers a nickel-copperchromium hydrogenation catalyst described in U.S. Pat. No. 3,152,998.
In contrast to the prior art, the hydrogenation step of the present process is preferably carried out in the presence of sulfur insensitive catalysts. Transition metal sulfide based catalysts are particularly preferred. For example, a CoS/MoS catalyst is used to advantage. In general, such catalysts result in the conversion of the sulfur compound impurities and their removal as hydrogen sulfide.